Researchers led by Tajuki Narumi at the University of Tokyo created a cookie-eating simulator that allows users to believe that they're tasting different flavors, when they're really only tasting one:

To create the effect, the team branded a plain cookie with a distinct logo that the headset tracks via a built-in camera. An air pump sprays out the smell of the chosen cookie, increasing its concentration as the system "sees" the cookie approaching the wearer's nose.

Meanwhile, a visual display in the headset shows an image of the chosen cookie, suggesting the correct texture for that flavour.

The combination of smell and visual texture combine to fool the user's sense of taste into thinking they are eating a flavoured cookie instead of the plain one.